[PATCH v1 3/4] usb: serial: mxuport: support serial interface mode configuration

Crescent Hsieh
2026-03-24T03:51:32Z

Add support for configuring the serial interface mode through
TIOCSRS485 and TIOCGRS485 using struct serial_rs485.

Sanitize the requested RS-485 settings and map them to the device
interface modes before issuing the vendor command to the firmware.

This allows userspace to switch between RS232, RS422, 2-wire RS485,
and 4-wire RS485, and to query the current per-port configuration.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
---
drivers/usb/serial/mxuport.c | 86 ++++++++++++++++++++++++++++++++++++
1 file changed, 86 insertions(+)

diff --git a/drivers/usb/serial/mxuport.c b/drivers/usb/serial/mxuport.c
index 4d29a431cefd..9a8bb4f02da3 100644
--- a/drivers/usb/serial/mxuport.c
+++ b/drivers/usb/serial/mxuport.c
@@ -183,6 +183,7 @@ struct mxuport_port {
u32 hold_reason;
u8 mcr_state; /* Last MCR state */
u8 msr_state; /* Last MSR state */
+ struct serial_rs485 rs485;
struct mutex mutex; /* Protects mcr_state */
spinlock_t spinlock; /* Protects msr_state */
};
@@ -1348,6 +1349,90 @@ static int mxuport_open(struct tty_struct *tty, struct usb_serial_port *port)
return err;
}

+static void mxuport_sanitize_serial_rs485(struct serial_rs485 *rs485)
+{
+ if (!(rs485->flags & SER_RS485_ENABLED)) {
+ memset(rs485, 0, sizeof(*rs485));
+ return;
+ }
+ if (rs485->flags & SER_RS485_MODE_RS422) {
+ rs485->flags &= (SER_RS485_ENABLED | SER_RS485_MODE_RS422);
+ return;
+ }
+ rs485->flags &= (SER_RS485_ENABLED | SER_RS485_RX_DURING_TX);
+
+ memset(rs485->padding, 0, sizeof(rs485->padding));
+}
+
+static int mxuport_rs485_config(struct usb_serial_port *port,
+ struct serial_rs485 *rs485)
+{
+ struct usb_serial *serial = port->serial;
+ u16 mode = MX_INT_RS232;
+
+ if (rs485->flags & SER_RS485_ENABLED) {
+ if (rs485->flags & SER_RS485_MODE_RS422)
+ mode = MX_INT_RS422;
+ else if (rs485->flags & SER_RS485_RX_DURING_TX)
+ mode = MX_INT_4W_RS485;
+ else
+ mode = MX_INT_2W_RS485;
+ }
+
+ return mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_INTERFACE, mode,
+ port->port_number);
+}
+
+static int mxuport_get_rs485_config(struct usb_serial_port *port,
+ struct serial_rs485 __user *rs485)
+{
+ struct mxuport_port *mxport = usb_get_serial_port_data(port);
+
+ if (copy_to_user(rs485, &mxport->rs485, sizeof(mxport->rs485)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static int mxuport_set_rs485_config(struct usb_serial_port *port,
+ struct serial_rs485 __user *rs485_user)
+{
+ struct mxuport_port *mxport = usb_get_serial_port_data(port);
+ struct serial_rs485 rs485;
+ int ret;
+
+ if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
+ return -EFAULT;
+
+ mxuport_sanitize_serial_rs485(&rs485);
+
+ ret = mxuport_rs485_config(port, &rs485);
+ if (!ret)
+ mxport->rs485 = rs485;
+
+ if (copy_to_user(rs485_user, &mxport->rs485, sizeof(mxport->rs485)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static int mxuport_ioctl(struct tty_struct *tty,
+ unsigned int cmd,
+ unsigned long arg)
+{
+ struct usb_serial_port *port = tty->driver_data;
+ void __user *uarg = (void __user *)arg;
+
+ switch (cmd) {
+ case TIOCGRS485:
+ return mxuport_get_rs485_config(port, uarg);
+ case TIOCSRS485:
+ return mxuport_set_rs485_config(port, uarg);
+ }
+
+ return -ENOIOCTLCMD;
+}
+
static void mxuport_close(struct usb_serial_port *port)
{
struct usb_serial *serial = port->serial;
@@ -1421,6 +1506,7 @@ static struct usb_serial_driver mxuport_device = {
.calc_num_ports = mxuport_calc_num_ports,
.open = mxuport_open,
.close = mxuport_close,
+ .ioctl = mxuport_ioctl,
.set_termios = mxuport_set_termios,
.break_ctl = mxuport_break_ctl,
.tx_empty = mxuport_tx_empty,
--
2.43.0